Insulated electrode for spark plugs



Patented Jan. 6, 1925.

WILLIAM S. THOMAS, 0F ROSELLE PARK, NEW JERSEY.

INSULATED ELECTRODE FOR SPARK PLUGS.

Application filed November 16, 1920. Serial No. 424,485.

To all whom it may concern:

Be it known that I, WILLIAM S. THOMAS, a citizen of the United States, residin at Roselle Park, in the county of Eliza%eth and State of New J ersey. have invented certain new and useful Improvements in Insulated Electrodes for Spark Plugs, of which the following is a specification.

One object of my invention is to provide an improved insulated electrode for use in spark plugs and to so construct my improve-l insulated electrode that it will include as a part of the insulating means, a mica tube which is so located and housed as to be free of contamination which would destroy its properties as an ideal insulator.

Another object is to so make my improved insulated electrode that it can be quickly and easily manufactured and will stand up under every condition to which a spark plug is subjected.

These objects, and other advantageous ends which will be described hereinafter, if attain in the following manner, reference being had to the accompanying drawings in which- Figure 1 is an elevation, shown partly in central longitudinal section, illustrating my present invention,

Figure 2 is an enlarged fragmentary view showing certain of the features of my invention,

Figure 3 is a fragmentary elevation, partly in section, illustrating certain of the parts in positions which they assume during the making of the device, and

Figure 4 is a perspective view of a ring or disk which I preferably employ in carrying out my invention.

Referring to the drawings, 5 represents an insulator casing which may be made of porcelain and which includes a cavity 6 which extends downwardly from its top surface 7 in cylindrical formation for a part of its length and thentapers downwardly as shown at 8; said tapered portion of the cavity being formed below the annular flange 9 which is usually present in insulated electrodes of this general character for connection in the body portion of the spark plug. The bottom of the tapered portion 8 of the cavity 6 terminates in a hole 10 which leads downwardly to the bottom surface 11. A connecting head 12 has a depending tenon portion 13 which fits Within the upper portion of the cavity 6 and is preferably cemented therein to entirely seal the upper part of the cavity. From the tenon 13 depends an electrode rod 14; said electrode rod extending entirely through the cavity and outwardly through the hole 10 to provide a sparking portion 15. A disk 16 is mounted on the electrode rod 14 and has its peripheral edge surface in tight fitting engagement with the inner wall of the tapered portion 8 of the cavity 6. This disk 16 is preferably made of steel and as will hereinafter be more definitely described is placed upon the electrode rod prior to the insertion of the electrode rod into the insulator casing. A tube 17 of mica, which is preferably formed by rolling a sheet of mica, fits the cavity 6 between the disk 16 and the inner end surface 17 of the tenon .13. This tube 17 has an internal diameter exceeding the external diameter of the portion of the electrode rod between the disk 16 and the tenon 13; the arrangement being such that said portion of the electrode rod extends centrally through said tube so that it does not contact therewith within the length of the mica tube as clearly shown in Figure 1.

In carrying out my invention, the mica tube 17 is made by winding a strip of thin mica to produce a tubular form after which the same is coated internally and externally by a cement preferably including a silicate base such for example as potassium silicate or sodium silicate. The tube thus coated is then baked in order to drive the cement in any of the crevices and interstices which may exist in the mica and between the wrappings thereof. The tube is then permitted to cool and is slipped over the electrode wire and the disk or ring 16 is forced upon the wire; said diskhaving a coating 18 of cement for engaging the end 19 of the mica tube 17.

In applying the disk to the electrode rod, the disk is provided with a hole 20 slightly less in diameter than the electrode rod 14 so that it is necessary to apply considerable pressure in order to force the disk on the rod. The disk is forced into contact with the end 19 of the mica tube and the entire structure is inserted within the cavity 6 of the insulator casing 5 so that the disk 6 will jam against the inner wall of the tapered portion 8; the lower portion of the electrode rod extending through the hole 16. The tenon 16 and head 12 may be cemented jacent end of the tube to the top portion of the insulator casing and in this manner the mica tube will be confined and sealed within the insulator casing so that it will be impossible for the mica tube to become saturated with any oils or products of combustion and an ideal insulator is thus provided by the mica tube so that transverse current leakage or short circuiting is practically impossible irrespective of the use to which the device is ut. p By carrying out the construction and arrangement as above described, the cement on the disk will coat and adhere to the adand thereby perform the two-fold function of closing the end of the tube and serving as a means for keeping the disk in connection with the mica tube. Furthermore the electrode cannot possibly become oxidized to increase its electrical resistance within the zone of the mica tube. Nor can it be coated with carbon or other deposit which would increase its electrical resistance. Thus the electrode within the body portion of the insulating casing is prevented from heating up to any such degree as to cause deterioration of the metal or any other condition which would impair the device for sparking purposes. Furthermore by constructing the parts as above described, ample freedom is permitted to the electrode rod or adjacent parts in order to expand or contract with the variation of heat imposed upon them and even though the electrode rod is not in tight fitting engagement with the inner surface of the wall 11, it is impossible for oils or products of combustion to attack the mica tube or pass to the portion of the electrode rod within the zone of the mica tube.

While I have described my invention as taking a particular form, it will be understood that the various parts of my invention may be changed without departing from the spirit thereof, and hence I do not limit myself to the precise construction set forth, but consider that I am at liberty to make such changes and alterations as fairly come within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is '1. A device of the character described including an insulator casing having a central cavity terminating in an inward taper; an

electrode rod extending through the casing; a disk carried by the rod and engaging with the taper, and a tube of a rolled continuous sheet of mica coated with cement surrounding the electrode rod and forming an air space therearound and having its inner edge cemented to the disk, substantially as described.

2. A device of the character described including a casing having a cavity extending downwardly from its top and terminating in a downwardly tapered portion; a cap having a depending portion insertable in the top of the cavity, an electrode rod extending through the cavity downwardly from the depending portion; a disk on the rod and supported by the walls of the tapered portion; and a mica tube surrounding the electrode rod between the depending portion and the disk.

3. A device of the character described including a casing having a cavity extending downwardly from its top and terminating in a downwardly tapered portion; a cap having a depending portion insertable in the top of the cavity, tending through the cavity downwardly from the depending portion; a disk on the rod and supported by the walls of the tapered portion; and a mica tube surrounding the electrode rod and in spaced relation with respect thereto between the depending portion and the disk.

4. A device of the character described in cluding a casing having a cap cemented in its top to seal the same and having a cavity extending downwardly from said cap and terminating in a downwardly tapered portion, there being a cavity extending downwardly from the tapered portion to the bottom of the casing, an electrode rod fastened to and extending from the inner sealed side of said cap and having a portion extending through said cavities, and a tube treated with material to prevent saturration with foreign matter surrounding the portion of the electrode rod in one of the cavities and in spaced relation with respect thereto.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

WILLIAM S. THOMAS.

Witnesses:

ELIZABETH GARBE, CHAS. E. Po'rrs.

an electrode rod ex- 

